Te…O Chalcogen Bonding in Supramolecular Chemistry

Abstract

Noncovalent interactions have attracted significant attention in the recent decades, both seeking a fundamental understanding and pursuing a wide range of applications. One particular case that has been studied in great detail is halogen bonding (XBs). The use of chalcogen bonding (ChBs) is only beginning to thrive but already has made a mark in the chemical community. In this thesis, we intended to augment the study of ChBs by examining 1,2-chalcogenazole 2-oxides. These N-oxides of C3NCh (Ch = Se, Te) heterocycles spontaneously assemble supramolecular structures through reversible Te…O ChB interactions. In solution, their macrocyclic tetramers and hexamers exist in equilibrium. These rings as well as supramolecular polymers (infinite chains in crystalline phase) have been authenticated by single-crystal X-ray diffraction. Despite the reversibility of the Te…O link, the macrocycles display properties typical of covalent macrocycles, including ability to coordinate metal ions, host small molecules, and form adducts with fullerenes. The compounds are stable to tellurium halogenation and unreactive to Lewis bases. However, they are readily cleaved by Brønsted and Lewis acids. Transformation of the structure of iso-tellurazole N-oxides by formal insertion of an aromatic bridge between the nitrogen and oxygen atoms led to a new family of supramolecular building blocks. A disubstituted benzene bridge yielded three isomers, all of which display signs of aggregation in solution and crystallize in either polymeric or macrocyclic aggregates. Among the latter, the ortho compound assembled a calixarene-like trimer while the para derivative built a macrocyclic tetramer akin to a molecular square.